The invention of this application is related in subject matter to concurrently filed application Ser. No. 873,639, entitled "Crossover Duct Assembly" in the name of Hsin-Juan Lui.
This invention relates to machines such as turbine engines and the like including multiple stage compressors. More specifically, this invention relates to a pneumatic crossover duct for providing flow-efficient communication between adjacent stages of a multiple stage compressor.
In the prior art, multiple stage compressors are found in a wide variety of applications. For example, a dual or multiple stage compressor is commonly used for supplying compressed charge air to a combustor section of a turbine engine. That is, ambient air is compressed by a first compressor, and then ducted to a second or subsequent compressor for obtaining increasingly higher levels of compression. Then, the highly compressed charge air is supplied to the engine combustor section including a combustion chamber for admixture with a suitable turbine fuel. The air-fuel mixture in the combustion chamber is ignited, and the hot products of combustion are utilized to rotate one or more turbine wheels at high speeds to obtain a relatively high power engine output.
In many multiple stage compressors, one or more centrifugal-type compressor wheels are commonly used. Such compressor wheels function to convert an axially entering gas stream into a radially outwardly directed compressed stream. With centrifugal compressor wheels, a generally annular pneumatic crossover duct is necessarily provided between compressor stages for turning the compressed gas from a radially outward direction back toward the next compressor stage in series for further compression. In such pneumatic crossover ducts, aerodynamic considerations are of high importance in that it is desirable to couple the compressed gas stream to subsequent compressor stages with a minimum of flow turbulence, and with a minimum of efficiency losses and a minimum of pressure losses.
Crossover ducts found in the prior art typically comprise an annular duct having a generally U-shaped cross section for turning a radially outward gas flow to a radially inward direction. A series of circumferentially spaced vanes are often included in the curved end portion, or turning bend, of the duct for assisting in turning the gas flow. See, for example, U.S. Pat. No. 3,361,073. The use of such turning vanes assists in reducing some flow turbulence, but it has been found that turning vanes also tend to interfere with gas flow and thereby create undesirable pressure losses. Accordingly, some prior art crossover duct constructions omit the turning vanes. See, for example, U.S. Pat. Nos. 2,661,594 and 2,620,626. However, even without turning vanes, prior art crossover ducts have been formed on a radial configuration which has been found to enhance undesirable boundary layer flow conditions resulting in undesirable efficiency losses.
Some prior art crossover duct constructions have included a series of circumferentially spaced diffuser blades or vanes in the gas entrance portion of the duct upstream of the turning bend for purposes of enhancing smooth gas flow. Typically, these diffuser blades comprise relatively sturdy blades having a substantially planar or slightly arcuate configuration within the duct to guide the compressed swirling gas flow in a radially outward direction. See, for example, U.S. Pat. Nos. 2,797,858; 2,827,261; 2,967,013 and 3,409,340. Prior art diffuser blades have been formed relatively thick to provide structural rigidity between the inner and outer walls of the crossover duct, and are typically anchored in the desired position by bolts, pins, or the like. However, for optimum aerodynamic performance it is desirable to provide a sturdy crossover duct construction which does not reply upon the diffuser vanes for structural rigidity, but instead uses relatively thin diffuser vanes shaped for minimum pressure losses and which may be formed from a relatively inexpensive and commercially available sheet material.
This invention overcomes the problems and disadvantages of the prior art by providing a structurally sound crossover duct construction having a vaneless turning bend configured to maximize efficiency and to minimize pressure losses, and including thin diffuser vanes shaped aerodynamically for improved flow efficiency and reduced pressure loss characteristics.